The present invention relates to a variable valve-timing device for internal combustion engines, particularly to a cam structure including a high speed cam with a high speed rocker arm for high speed operation of engine and a low speed cam with a low speed rocker arm for low speed operation of engine.
Conventionally, operating engine valve-timing is fixed by design. However, it is a well-known drawback that low speed engines are unable to perform properly at high speed and that high speed engines are inefficient at low speed. In order to obtain an excellent performance at both low speed and high speed for both low speed engines and high speed engines, even any type of engine, the timing of valves should be variable in response to the speed of the engine and other factors, such as engine load, the speed of car, and water temperature of cooling system, etc. In other words, the opening time of intake and exhaust valves should increase or decrease in response to an increase or a decrease of engine speed and other factors. The present invention intends to provide a variable valve-timing structure to eliminate the above mentioned problems and to provide for economical fuel consumption.